Let k be an integer. Two words u and v of the same length are k-abelian equivalent, if they have the same prefix (resp. suffix) of length k-1 and if, for all words x of length k, the numbers of ... [more ▼]

Let k be an integer. Two words u and v of the same length are k-abelian equivalent, if they have the same prefix (resp. suffix) of length k-1 and if, for all words x of length k, the numbers of occurrences of x in u and v are the same. This notion has received some recent interest, see the works of Karhumäki et al. The k-abelian complexity of an infinite word x maps an integer n to the number of k-abelian classes partitioning the set of factors of length n occurring in x. The Thue-Morse word is a well-known and extensively studied 2-automatic sequence. It is trivially abelian periodic and its (1)-abelian complexity takes only two values. The aim of this talk is to explain how to compute the 2-abelian complexity a(n) of the Thue-Morse word, showing in particular that it is unbounded. We conjecture that a(n) is 2-regular in the sense of Allouche and Shallit. This question can be related to a recent work of Madill and Rampersad where the (1)-abelian complexity of the paper folding word is shown to be 2-regular. We will also explain why the usual logical framework introduced by Büchi and popularized by Bruyère (indeed, automatic sequences can be characterized in an extension of the Presburger arithmetic) and the recent work of Charlier et al. about "automatic theorem-proving" of properties of automatic sequences cannot be applied to these questions related to abelian complexity. [less ▲]

Human T-lymphotropic virus type 1 (HTLV-1) is a retrovirus that infects about twenty million individuals worldwide. HTLV-1 is the causative agent of different diseases among which the most common are the ... [more ▼]

Human T-lymphotropic virus type 1 (HTLV-1) is a retrovirus that infects about twenty million individuals worldwide. HTLV-1 is the causative agent of different diseases among which the most common are the adult T-cell leukemia (ATL) and a neurodegenerative disorder called HAM/TSP (Human associated myelopathy/ Tropical spastic paraparesis). A key parameter of HTLV-1 pathogenesis is faster replication of provirus-carrying lymphocytes allowing clonal expansion of infected cell populations. The virally-encoded Tax oncoprotein plays an essential role in this process by interacting with DNA replication origins and accelerating S phase progression. By reprogramming the timing of origin firing, Tax also creates a replicative stress leading to DNA double strand breaks. This mechanism further triggers the DNA damage response (DDR) that induces cell cycle arrest and initiates either apoptosis or senescence. However, HTLV-1 infected cells have developed strategies to interfere with the DDR and are adapted to checkpoint control. These cells are thus able to proliferate despite occurrence of DNA damage. Based on these observations, we now propose a novel therapeutic approach based on the principle of synthetic lethality. [less ▲]

The negative impacts linked to the introductions of the multicolored Asian ladybeetle, Harmonia axyridis (Pallas), progressively increasing in Europe and in North America, it is urgent to find a way to ... [more ▼]

The negative impacts linked to the introductions of the multicolored Asian ladybeetle, Harmonia axyridis (Pallas), progressively increasing in Europe and in North America, it is urgent to find a way to manage its populations. The social interactions involved in its aggregative behavior remain misunderstood although a better understanding of the semiochemicals the ladybeetles use during this phenomenon could lead to the development of new control methods. Therefore, the main objective of this thesis was to improve the understanding of the mechanisms set up by H. axyridis during its aggregative stage. Firstly, we have demonstrated the use of two different area markings by this species during its overwintering. The first one, laid by the ladybeetles while walking, lead conspecifics towards aggregation sites whereas the second one, deposited inside these sites, ensures the cohesion of the cluster. These markings are made up of saturated, mono- and diunsaturated hydrocarbons. Among these chemicals, it seems that the unsaturated hydrocarbons, and in particular the ones containing two double bonds, present a greater biological activity. However, the response of H. axyridis towards these chemicals depends on the insect physiological state. In the second instance, we have showed for the first time that H. axyridis presents a permanent aggregative behavior. The hydrocarbons laid by the ladybeetles during their displacements do not play any role in this behavior during summer conditions. On the other hand, conspecific elytral compounds and, in a lesser extent, physical contact, are well involved. Moreover, all our experiments have pointed out that visual elements play a major role in this social behavior and so, have also to be taken into account in the design of traps to control the populations of this invasive species. [less ▲]